Method of recovering fatty acids



ug.- 29, 1939I- I o. M.URBA|N ET AL 2,171,200

METHOD OF RECOVERING FATTY ACIDS Filed Feb. 13, 1957 Patented Aug. 29, 1939 PATENT OFFICE 2,171,200 METHOD oF REoovEmNG FATTY Aoms Oliver M. Urbain and William R.. Stemen, Columbus, Ohio, assignors to Charles H. Lewis, Harpster, Ohio Application February 1 7 Claims.`

This invention relates to a process for recovering fatty acids from solutions containing the same. In its more specific aspect, the invention contemplates the recovery of the fatty acids present in the soaps discharged in waste waters from laundries and the like.

It is well-known that the wash waters or suds employed in laundering operations contain from 0.25 gram to 5.0 grams of fatty acids per liter. These fatty acids are, of course, present in the form of sodium and potassium salts, that is, in the form of soaps. In addition to soaps, the laundry wastes contain so-called soap builders, free alkali, dirt, dyes, greases, starch, carbohydrates, lint, and other cellulosic materials as well as various forms of bacteria.

The present process is primarily concerned with the steps of freeing the fatty acids from the soaps and recovering the same from the waste solution. The fatty acids may be released from the soap by effecting hydrolysis thereof through the addition of a dilute acid such as dilute hydrochloric to the waste.

When dilute hydrochloric acid is added to laundry waste or the like, the fatty acids are released from the soaps according to the following general reaction:

R.COO.Na-lHCl- R.COOH+NaCl v Soap Fatty acid 3Q A specific example of the general reaction above is given as follows:

C17H35.COO.Na-HClCi'iHsaCOOH-l-Nacl Sodium stearate Stearic acid The above reactions take place at all pHs below pH 7.0, but even at pHs above pI-I 7.0 the soaps hydrolyze according to the following general reaction:

R.COO.Na-|-H2OR.COOI-I+N0OH Soap Fatty acid It should be noted that this reaction is of the reversible type. If the fatty acid formed on the right is removed, the hydrolysis of the soap will proceed to completion. In other words, as long as the pressure is eliminated from the right side of the reaction, it will continue to move to the right.

' A specific example of the hydrolysis of a is given in the followingv reaction:

Sodium palmitate Palmitic acid Comingnow to a description of the present process, reference will be hadl to the accompany- Q ing drawing for clarification, wherein:

SO ap 3, 1937, Serial No. 125,668

Figure 1 is a diagrammatic iiow chart representing the various steps in the process; and

Figure 2 is a more or less diagrammatic illustration of a suitable filter structure for employment in removing the fatty acids.

Referring to the drawing, the waste containing the recoverable fatty acids is first passed through a screening unit to free the same of entrained solids and thence preferably passed through a coarse sand filter to remove such solids as might otherwise foul the subsequent chemical filter unit. There is added to the Waste a dilute acid, such as hydrochloric acid, to induce hydrolysis of the contained soaps. The solution is then passed into a filter for removing fatty acids.

The nature of the filtering medium employed for removing the fatty acids constitutes an important feature of the present invention. In the present process, the filtering medium employed for elfecting remo-val of the fatty acids released from the soaps as a result of hydrolysis due to the addition of the dilute acid comprises the hydrous oxides employed at or below their individual iso-electric points. We have ascertained that all hydrous oxides will function satisfactorily in the present process when employed at or below their iso-electric points.

Hydrous oxides are colloidal materials formed by the hydrolysis of heavy metal salts. Some cli-valent metal salts will hydrolyze to give hydrous oxides, but all cli-valent metal salts do not so act. All of the tri-valent metal salts do hydrolyze to give hydrous oxides as well as all higher valent metals. In our process we prefer to employ the tri-valent metal salts having a negative atom or radical with a valence of one, such, for example, as ferrie chloride, nitrate or acetate, or stannic chloride or titanium, antimony or cesium chlorides.

To produce the hydrous oxides and lower them to their iso-electric points is a comparatively simple procedure. The general reaction for the hydrolysis of a heavy metal salt is given as follows:

nMAz-l-nI-I2O61LMIM(OH) ayMAz] -|rLHA in which-f M=a heavy metal e=a number equivalent to the valence of M n=a whole number A=a negative atom or radical A specific exampleof the hydrolysis of a heavy metal salt is given as follows: l

The numerical values for :c and y in both reactions given above will vary with the pH of the hydrolysis medium. As the pH of the medium increases above pH '7.0, the value of a: increases and the value of y decreases, and as the pH of the medium decreases below pH 7.0, the value of x decreases and the Value of y increases. At pH 11.5 the value of y is zero, and at pH 2.5 the value of x is Zero.

From the above reactions it is seen that the hydrous oxides are either adsorption products or addition compounds.

For purposes of illustration, the iso-electric points of a few of the hydrous oxides are listed below. It will be observed that the last two enumerated metals are di-valent:

Metal Iso-electric pH After the charge on the hydrous oxides has been neutralized to bring them to their iso-electric point, it is impossible to recharge these materials by manipulation of the hydrogen ion concentration of the medium. This is the reason for employing the same at or below the iso-electric point.

For purposes of illustration, We will describe the preparation of a filtering medium for removal of the fatty acids in which we employ hydrous ferrie oxide since it is an especially economical one of the hydrous oxides available for use in our process. It is to be understood that precisely the same procediue may be followed in preparing the filtering medium when employing any of the other hydrous oxides.

The carrier for the hydrous oxide employed will preferably constitute either hard coke or magnesia silicate brick. Both of these materials have an enormous surface area and are both extremely porous and relatively inert chemically. Additionally they will both withstand high temperatures and yet maintain their physical structures. The filtering medium for use in our process is preferably in the form of a granular mass, the individual granules of which will pass a five-mesh screen and be retained upon a twenty-mesh screen.

To obtain the filtering medium impregnated with and carrying the hydrous oxide, the carrier is pickled in a concentrated solution of ferrie chloride, for example, until thoroughly saturated. The excess reagent is then drawn off, and the granulated mass is passed through an atmosphere of ammonia without drying, and in this manner the hydrous oxide is brought down to its iso-electric point or below. It will be appreciated that at this point the granular carrier is thoroughly impregnated with hydrous ferric oxide. The mass is then dried in a current of warm air at about 120 C. to set the oxide. The filtering material is then ready for use.

The apparatus instrumentalities employed in carrying out the process of the present invention are more or less conventional and relatively unimportant to the process. It is accordingly not believed necessary that they be specifically illustrated. The screening unit is employed tov remove the heavy suspended matter from the waste. Such screens are self-discharging, and the solids removed by the screens may be flushed directly into a suitable sewer or the like.

The mechanical sand filter is employed to remove suchsuspended matter as passes the screens and to insure that no suspended matter will pass into and foul the fatty acid recovery unit. The sand filter can, of course, be equipped with a conventional back-wash through the medium of which it may be back-washed with clear water after each days run. The back-wash water will, of course, carry the solids from the sand filter and may be likewise discharged into a suitable sewer or the like.

A suitable construction for the fatty acid recovery unit is illustrated in Figure 2 wherein the filtering chamber is designated generally at I and constitutes a suitable sheet metal container since it isv not required to withstand excessive pressure or temperature conditions. The chamber I is provided with a filtering medium carrying grate 2 suitably supported on members 3, the filtering agent diagrammatically illustrated at 4, and the line 5 through which the solution containing the fatty acids to be recovered is introduced to the filtering chamber.

The filtrate leaves the bottom of the chamber through the line 6 and may be discharged through branch line 'I controlled by the valve 8 for further treatment or into a sewer as may be desired. A steam line 9 extends into the bottom of the chamber I and is provided with a perforated extension Ill for delivering steam below the filtering medium for the purpose of driving olf the fatty acids from the filter. The steam carrying its fatty acid content leaves the top of the filter through line II controlled by valve I2 and passes tothe condenser I3. The condensate is then delivered through line I4 to a suitable evaporating unit I5 wherein the water is driven off through the line IB and the fatty acids are recovered.

Oftentimes during the introduction of steam to the filtering chamber I, condensation occurs in the filtering medium, and the condensate carrying some of the fatty acids passes out through the line 6. In this case the valve 8 can be closed and this condensate passed through the by-pass line I1 controlled by the valve I8 and introduced tothe line I4 to flow with the condensate from the condenser I3 to the evaporator I5.

It will be understood that the process is not dependent upon this particular form of apparatus, nor is the invention to be limited by the foregoing description beyond the scope of the subjoined claims.

Having thus described the invention, what we claim is:

1. In a process for recovering fatty acids from solutions containing the same, the steps comprising'eiecting chemical removal of the fatty acids by passing such solutions through a filter charged with an hydrous oxide at or below its isoelectric point and thereafter effecting recovery of said fatty acids by treatment of the hydrous oxide filter.

2. In a process for recovering fatty acids from solutions containing the same, the steps comprising effecting chemical removal of the fatty acids by passing such solutions through a filter charged with hydrous ferrie oxide at or below its isoelectric point and thereafter effecting recovery o f said fatty acids by treatment of the hydrous ferric oxide filter.

3. In a process for recovering fatty acids from solutions containing the same, the steps comprising effecting chemical removal of the fatty acids by passing such solutions through a lter charged with hydrous stannc oxide at or below its isoelectric point and thereafter effecting recovery of said fatty acids by treatment 4of the hydrous stannic oxide filter.

4. A process for the recovery of fatty acids from solutions containing the same comprising effecting chemical removal of the fatty acids by passing the solutions through a filter charged with a hydrous oxide at or below its isoelectric point, thereafter passing steam through the filter to free the fatty acids from the filter and carry them over to a condenser, and finally evaporating the water from the resulting condensate and recovering the fatty acids as a product of the process.

5, A process for recovering fatty acids from soap solutions comprising adding a dilute acid to the soap solution to release the fatty acids from the soap by hydrolysis, passing the solution through a filter charged with an hydrous oxide at or below its isoelectric point to chemically remove the fatty acid product of the hydrolysis reaction, and finally recovering the fatty acids from the filter.

6. A. process for recovering fatty acids from laundry waste comprising adding to they waste a quantity of HC1 to effect hydrolysis of the soap solution and reiease of the fatty acids, chemically removing the fatty acids as released by effecting the hydrolysis in the presence of an hydrous oxide carrying reagent at or below its isoelectric point, and nally recovering the fatty acids from said liydrous oxide carrying reagent.

7. In a process for recovering fatty acids from solutions containing the same, the steps comprising effecting chemical removal of the fatty acids by passing the fatty acid solution through a filter composed of substantially inert granular material impregnated with an hydrous oxide at or below its isoelectric point and thereafter effecting recovery of said fatty acids by treatment of the hydrous oxide filter.

OLIVER M. URBAIN. WILLIAM R. STEMEN. 

